Dryer control system using moisture sensor and semiconductors to control cycle

ABSTRACT

A dryer control system for sensing the moisture content of clothes which bridge a pair of spaced apart sensing electrodes in a dryer employs means for adjusting the desired moisture retention, means for adjusting the moisture sensitivity of the circuit and the duration of a drying time period at the end of the dryer cycle, and means for rendering the system circuit insensitive to false indications caused by static charges applied across the moisture sensing electrodes. The system circuit is employed to directly control turn-off of the drive motor and heating means of a dryer and includes a further means for delaying for selected intervals termination of the drying cycle upon detection of the desired moisture retention condition.

[ 1 Sept. 18, 1973 1 DRYER CONTROL SYSTEM USING MOISTURE SENSOR AND SEMICONDUCTORS TO CONTROL CYCLE [75] Inventor: Joseph Karklys, Saint Joseph, Mich.

[73] Assignee: Whirlpool Corporation, Benton Harbor, Mich.

221 Filed: Nov. 12,1971

[21] Appl.No.: 198,198

3,331,139 7/l967 Finnegan et al. 34/45 Primary ExaminerMeyer Perlin Assistant ExaminerPaul Devinsky Attorney-James S. Nettleton et al.

[57] ABSTRACT A dryer control system for sensing the moisture content of clothes which bridge a pair of spaced apart sensing electrodes in a dryer employs means for adjusting the desired moisture retention, means for adjusting the moisture sensitivity of the circuit and the duration of a drying time period at the end of the dryer cycle, and means for rendering the system circuit insensitive to false indications caused by static charges applied across the moisture sensing electrodes. The system circuit is employed to directly control turn-off of the drive motor and heating means of a dryer and includes a further means for delaying for selected intervals termination of the drying cycle upon detection of the desired moisture 15 Claims, 6 Drawing Figures [52] [1.8. CI. 34/45, 34/48 [51] Int. Cl F261) 19/00, G051) 11/00 [58] Field of Search 34/45, 48; 318/483; 307/118, 93; 73/73, 76

[56] References Cited UNITED STATES PATENTS 3,660,909 5/1972 WillCOX 34/45 3,621,293 11/1971 Heidtmann 307/252 N 3,521,376 BBIICI' retention condition 3,460,267 8/1969 Lorenz.... 34/45 3,402,478 9/1968 Hetrick 34/53 5/ L 5- C s2 N DJ L.-

PATENTED 3.758.959

SHEET 2 BF 2 FIG. 20 T V WWW FIG. 2b 7 FIG. 2c TH A FIG. 2d

1 NVEN TOR.

DRYER CONTROL SYSTEM USING MOISTURE SENSOR AND SEMICONDUCTORS TO CONTROL CYCLE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a dryer control system which eliminates the use of a mechanical timer and improves dryness sensing, and is more particularly concerned with providing such a dryer control system which is insensitive to static charges which would ordinarily provide false dryness indications.

2. Description of the Prior Art It has been determined that static charges carried by a drying clothes load and applied across a pair of spaced sensing electrodes can cause a dryness sensing circuit to generate false signals indicative of a substantial moisture content. Heretofore, this problem has not been completely recognized or appreciated. The ability of static signals to render a moisture sensor inaccurate becomes even more pronounced when the moisture sensor is utilized in a dryer control circuit which employs semiconductor components which are sensitive to and operable in response to static signals.

SUMMARY OF THE INVENTION In view of the foregoing, it is therefore a primary object of the invention to provide a solid state dryer control circuit having means for rendering the moisture sensor thereof insensitive to static charges while permitting the control circuit to time out the drying cycle to completion after a moisture signal is no longer detected during a user selected time span.

The foregoing objective is realized for a moisture sensor having spaced apart electrodes through means including the provision of a diode and a capacitor connected in series across the moisture sensing electrodes to'block static signals of one polarity and filter out static charges of the opposite polarity.

Inasmuch as a dryer control circuit constructed in accordance with the principles set forth above would automatically terminate the drying operation upon detection of a desired moisture content, and inasmuch as it may be desirable to have a timed drying cycle available, particularly for use with bulky hard-to-dry articles, it is another object of this invention to provide a solid state timing apparatus which may be selectively interposed in the dryness signal train between the moisture sensing portion of the control circuit and the motor and heater turnoff portions of the control circuit for providing selected additional drying intervals upon detection of a preset moisture content. In a preferred embodiment of the invention, this objective is realized through the provision of a solid state counting circuit which is operable in response to a dryness signal to activate the motor and heater turn-off portion of the dryer control circuit. The counter in the preferred embodiment is provided as a cascade of binary circuits with the outputs thereof selectively connectible to the motor and heater turn-off portion of the control circuit, the selective connection being effected by means of a switch which accordingly selects a desired amount of additional drying time. The availability of additional drying time is most advantageously employed when damp portions of articles do not bridge the moisture sensor electrodes as could be the case in drying heavy articles such as towels, rugs and trousers with pockets, or the like, or where a stationary rack carrying the articles to be dried is disposed within the drum of the dryer.

BRIEF DESCRIPTION OF THE DRAWING Other objects, features and advantages of the invention, its organization, construction, and operation, will best be understood from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings, in which:

FIG. I is a schematic circuit diagram of a dryer control circuit constructed in accordance with the principles of the present invention;

FIG. 2a to FIG. 2d are a series of dryer curves showing the variation of the voltage across a portion of the dryer control circuit of FIG. 1 during the drying cycle, and with certain changes in the circuit of FIG. 1 to illustrate the advantages of the present invention; and

FIG. 3 is a schematic diagram of the added time base option for the dryer circuit of FIG. 1 whereby selected time delays may be interposed between the detection of a dry load and the deactivation of the drive motor and heater.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is illustrated in schematic form, a dryer control circuit for connection to a commercial supply line at terminals L1, L2 and N. Normally, the voltage across the terminals L1, L2 is 220/230 VAC and from L1 to N and L2 to N is /115 VAC. The heater circuit extends from the terminal L1 to the terminal L2 by way of a pair of relay contacts K2, K1, the heater HTR, a thermostat switch TH and a set of contacts K4, K3. The dryer control circuit components are powered over the lesser voltage circuit extending between the terminal L1 and the terminal N as follows.

A moisture sensing circuit for sensing moisture in a damp clothes load consisting of articles of fabric includes a moisture sensor S having a pair of moisture sensing electrodes S1, S2. Themoisture sensing electrode S2 is connected to the terminal N by way of a door operated switch D5 which is closed when the door of the dryer is closed, as is well known in the art.

It is a feature of the present invention that the dryer control circuit includes means for limiting the voltage across the moisture sensing electrodes S1, S2 to a DC voltage of relatively low magnitude so that the moisture sensor S can be connected into an integrated circuit. To this end the moisture sensing electrode S1 is connected to the terminal L1 by way of a resistor R1, a variable resistor RlV, a diode CR3, a resistor R9 and the set of contacts K1, K2. In the illustrated arrangement the voltage across the moisture sensing electrodes S1, S2 is 1.5 volts DC, thus resulting in a low voltage sensing circuit compatible with bipolar and metal oxide semiconductor (MOS) integrated circuit processes.

The moisture sensing circuit also includes a diode CR1 and a resistor R2 connected in series between the moisture sensing electrode S1 and the base of a transistor 01 which has its emitter connected to the terminal N and its collector connected to the aforementioned path to the terminal Ll by way of the diode CR3. A capacitor C1 is connected between the cathode of the diode CR1 and the terminal N by way of the door switch DS. The collector of the transistor O1 is connected to the base of a transistor Q2 whose emitter is connected to the terminal N and whose collector is connected to the aforementioned powering path by way of a resistor R4 and a variable resistor R4V. The transistor Q2 constitutes an inverter stage. A bias applied to the base of the transistor Q] by way of the resistor RlV, the resistor R1, the diode CR1 and the resistor R2 renders the transistor Q1 conductive which in turn causes the transistor Q2 to be non-conductive. As a damp clothes load consisting of articles of fabric bridges the moisture sensing electrodes 81, S2, the base-emitter bias of the transistor Q1 is shunted to render the transistor Q1 non-conductive and the transistor Q2 conductive. As the clothes load becomes drier, the shunting of the moisture sensing electrodes S1, S2 becomes higher in impedance to a point whereat the bias is again effective to cause the transistor Q] to become conductive. The sensitivity of the moisture sensing circuit may be adjusted by means of the variable resistor RIV.

As the clothes load becomes drier, static signals carried by the clothes may also be applied across the moisture sensing electrodes 81, S2. Therefore, means are provided for rendering such static signals ineffective. The diode CR1 blocks negative static signals while the diode CR1 and the capacitor C1 in series shunt the positive static signals to the terminal N, which is ordinarily connected to a good earth ground. The diode CR1 and the capacitor C1 in parallel with the sensor S therefore provide an effective means of filtering to eliminate static build-up and its attendant noise problems in the solid state circuit.

FIG. 2, consisting of dryer cycle curves showing the variation of the voltage across the junction between a charging capacitor C2 and a resistor R4 (see FIG. 1) and ground during the drying cycle, illustrates the effectiveness of the present invention to eliminate static build-up and its attendant noise problems during the drying cycle.

FIG. 2a shows the normal curve of a dryer cycle in drying a damp clothes load utilizing the diode CR1 to block negative static signals while the diode CR1 and the capacitor C1 in series shunt the positive static signals to the terminal N, as shown in the circuit of FIG. 1. As drying progresses the voltage wave form level increases in a regular pattern until it reaches a peak sufficient to fire a unijunction transistor Q3 resulting in termination of drying as will appear.

FIG. 2b shows the changes in the voltageduring the drying cycle for the circuit of FIG. 1 with the diode CR] shorted. FIG. 20 shows the changes in the voltage during the drying cycle for the circuit of FIG. 1 with the capacitor C1 disconnected. F'IG. 2d shows the changes in the voltage during the drying cycle for the circuit of FIG. 1 with the diode CR1 shorted and the capacitor C1 disconnected.

The curves of FIGS. 2b, 2c, and 2d, where the means for eliminating static build-up of the present invention was not used in the circuit, all show erratic, noise-filled patterns which would preclude an accurate sensing of moisture in the clothes load.

A relaxation oscillator is connected to and controlled by the inverter circuit of the transistor Q2. This oscillator comprises the resistor R4V, the resistor R4 and the charging capacitor C2 connected in series between the diode CR3 and the terminal N. When the transistor Q2 becomes non-conductive, the capacitor C2 charges over the resistor R4V and R4 up to a level which is sufficient to render a unijunction transistor Q3 conductive. The unijunction transistor Q3 has its emitter connected to the junction between the capacitor C2 and the resistor R4, one base connected to the diode CR3 by way of a resistor R5 and a second base connected by way of a resistor R6 to the common terminal N by way of the door switch DS. The frequency of pulsing, or the delay between the time that the transistor Q2 becomes non-conductive and the transistor Q3 becomes conductive may be adjusted by means of the variable resistor R4V. The resistor R4V and the resistor RlV may be mechanically linked or ganged together as shown in FIG. 1 to provide an adjustment of the delay between the time that the transistor Q2 becomes nonconductive and the transistor Q3 become conductive, i.e., the duration of a time period at the end of the dry cycle wherein if no moisture signal is received by the dryness sensor by the end of the time period, the drying cycle is terminated. This structure also provides an adjustment of the sensitivity of the moisture sensing circuit. In a preferred embodiment of the invention providing excellent performance, the variable resistors RlV and R4V are linked together so that proportional resistance portions of each of the resistors are connected into the circuit as the resistors are varied.

The relaxation oscillator is connected to the motor and heater turn-ofi circuit which includes a resistor R7, an SCR Q4, a diode CR2, a resistor R8, a triac Q5, a drive motor M and a relay K. The SCR Q4 has a gate electrode connected to the second base of the unijunction transistor Q3 and is rendered conductive upon the firing of the transistor Q3. The SCR Q4 will remain conductive until power has been removed from the circuit at the contacts K1, K2 as will be described below.

Normally, the triac O5 is conductive by virtue of having a gate electrode connected in a voltage divider circuit which extends from the cathode of the diode CR3 to the terminal N including the resistor R7, the diode CR2, the resistor R8 and the door switch DS. Firing of the SCR Q4 bypasses this biasing circuit to render the triac non-conductive which interrupts the powering circuit of the motor M and the relay winding K. Upon initiation of operation of the drying cycle and after closure of the door switch DS, a push button PB, generally located on a control console, isdepressed by an operator to mechanically close the contacts K1, K2 and the contacts K3, K4 to extend the potential at the terminal L1 to the moisture sensing circuit and to the heater circuit. The contacts K1, K2 provide a self-latching feature of the relay upon closure and energization of the winding K, that is, with the triac Q5 rendered conductive. When the triac O5 is rendered non-conductive,-by the firing of the SCR Q4, the energization of the motor M and the relay winding K is interrupted. This action releases the latch of the relay and permits the contacts K1, K2 and K3, K4 to open to remove power from the moisture sensing circuit (K1, K2) and from the heater circuit (K3, K4).

In FIG. 2a the initial portion of the dryer cycle, wherein the clothes load is damp and moisture signals are sensed by the moisture sensing circuit, is denoted by the reference character T1. The time period at the end of the cycle wherein it no moisture signal is re ceived by' the dryness sensor by the end of the time period, the drying cycle is terminated, is denoted by the reference character T2. The peak voltage where unijunction transistor Q3 becomes conductive is indicated by the reference character VP.

Referring to FIG. 3, means are illustrated for effecting a selected extended delay time before termination of the drying operation subsequent to sensing the desired moisture content. This means is in the form of a circuit which may be interposed between the relaxation oscillator and the motor and heater turn-off circuit of FIG. I, particularly between the points A and B. When this option is provided, a switch SW has a movable contact SW2 connected to the point A and a fixed contact SW1 connected to the point B. For the aforementioned type of operation of the circuit, the switch contact SW2 is placed in engagement with the switch contact SW1. If, however, the operator wishes to extend the drying time by a selected interval, the switch contact SW2 is moved away from the contact SW1 and into engagement with a contact SW3. A series of delay circuits TDl-TD4 is connected between the switch contact SW3 and the point B. These time delay circuits may form a simple frequency divider of bistable solid state circuits. Thus, the dryness sensing apparatus of FIG. 1 includes means comprising a relaxation oscillator for applying periodic reference signals to the series of time delay circuits TDl-TD4. Assuming the period of the relaxation oscillator to be four minutes, and assuming an extension of the drying period in four-minute increments, the output of each time delay circuit is connected to a separate contact of a selector switch SS which has a movable contact SS1 connected to the point B. The fixed contacts of the selector switch SS are identified by the drying time provided by the associated time delay circuits TDl-TD4 and therefore carry the reference characters SS4, SS8, S816 and S832 for 4, 8, l6 and 32 minute drying intervals.

Generally, then, there has been disclosed a solid state dryer control which, for the most part, is capable of being integrated on a single monolithic chip and which is generally insensitive to static buildup and its attendant noise problems so as to provide precise moisture sensing and improved accuracy. It further permits the elimination of the usual motor driven timer thereby decreasing cost.

Although I have described my invention by reference to a particular illustrative embodiment thereof, many changes and modifications of my invention may be made by those skilled in the art without departing from the spirit and scope thereof, and I intend to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of my contribution to the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

- 1. In a dryer control which is responsive to desired moisture content level in articles of fabric to end the drying period, and a dryness sensor circuit having a dryness sensor comprising a pair of spaced electrodes which may be bridged by an article of fabric undergoing drying, means for rejecting false signals caused by static electricity generated by the drying articles comprising means associated with said sensor for grounding one polarity of static signals and means associated with said sensor for blocking the other polarity of static signals, said means for blocking static signals including a diode connected to one of said electrodes, and said means for grounding static signals including a capacitor connected between said diode and ground, the other electrode being connected to ground.

2. In a dryer control according to claim 1, wherein said sensor circuit comprises means for adjusting the desired moisture level and means for adjusting the control sensitivity.

3. ln a dryer control according to claim 1, wherein said sensor circuit comprises first resistor means for es-. tablishing the desired moisture level and second resistor means for establishing the control sensitivity.

4. In a dryer control according to claim 1, wherein said sensor circuit comprises means for contemporaneously adjusting the desired moisture level and the control sensitivity.

5. ln a dryer control according to claim 4, wherein said means for contemporaneously adjusting the desired moisture level and the control sensitivity comprises a pair of ganged variable resistors connected in a circuit of the dryer control and mechanically linked together so that adjustment of the desired moisture level also provides an adjustment of the control sensitivity of the circuit.

6. In a dryer control according to claim 5, wherein the variable resistors are linked so that proportional resistance portions of each of the resistors are connected into the circuit as the resistors are varied.

7. In a dryer control according to claim 1, comprising means for selectively extending the drying period in time increments beyond the time required to reach the desired moisture content level.

8. In a dryer control according to claim 1, wherein the control includes means for limiting the voltage across the sensor to a DC voltage of relatively low magnitude so that the sensor can be connected into an integrated circuit.

9. Dryness sensing apparatus for controlling the operation of the drying means of a laundry appliance, comprising:

a dryness sensor including a pair of spaced electrodes for contacting an article of fabric undergoing drying, said electrodes connected across an electrical supply, a diode connected to one of said electrodes and a capacitor connected between said diode and the other of said electrodes which is connected to a reference potential of the electrical supply, said diode effective to block static signals of one polarity and pass via said capacitor static signals of the opposite polarity to the supply reference, means for establishing a desired moisture content level, and means connected to the junction of said diode and said capacitor for providing a control signal in response to the detection of the desired moisture content level; and

means connected to said dryness sensor and operable in response to said control signal to terminate operation of the drying means.

10. A dryness sensing apparatus according to claim 9, wherein said means for establishing a desired moisture content level includes adjustable means for changing the desired moisture content level.

11. A dryness sensing apparatus according to claim 9, wherein said means for providing a control signal includes adjustable means for varying its sensitivity to the sensed moisture content level.

12. A dryness sensing apparatus according to claim 9, wherein there is a series of time delay circuits connected between said dryness sensor and said means for terminating operation of said drying means to extend the drying time by selected intervals, and wherein said means for providing a control signal includes means for applying periodic reference signals to said series of time delay circuits.

13. A dryness sensing apparatus according to claim 9, wherein said means for establishing a desired moisture content level comprises means for adjusting the duration of a time period wherein if no moisture signal is received by the dryness sensor from the fabric undergoing drying by the end of the time period, the drying cycle is terminated. I

14. A dryness sensing apparatus according to claim providing a control signal and the drying means. 

1. In a dryer control which is responsive to desired moisture content level in articles of fabric to end the drying period, and a dryness sensor circuit having a dryness sensor comprising a pair of spaced electrodes which may be bridged by an article of fabric undergoing drying, means for rejecting false signals caused by static electricity generated by the drying articles comprising means associated with said sensor for grounding one polarity of static signals and means associated with said sensor for blocking the other polarity of static signals, said means for blocking static signals including a diode connected to one of said electrodes, and said means for grounding static signals including a capacitor connected between said diode and ground, the other electrode being connected to ground.
 2. In a dryer control according to claim 1, wherein said sensor circuit comprises means for adjusting the desired moisture level and means for adjusting the control sensitivity.
 3. In a dryer control according to claim 1, wherein said sensor circuit comprises first resistor means for establishing the desired moisture level and second resistor means for establishing the control sensitivity.
 4. In a dryer control according to claim 1, wherein said sensor circuit comprises means for contemporaneously adjusting the desired moisture level and the control sensitivity.
 5. In a dryer control according to claim 4, wherein said means for contemporaneously adjusting the desired moisture level and the control sensitivity comprises a pair of ganged variable resistors connected in a circuit of the dryer control and mechanically linked together so that adjustment of the desired moisture level also provides an adjustment of the control sensitivity of the circuit.
 6. In a dryer control according to claim 5, wherein the variable resistors are linked so that proportional resistance portions Of each of the resistors are connected into the circuit as the resistors are varied.
 7. In a dryer control according to claim 1, comprising means for selectively extending the drying period in time increments beyond the time required to reach the desired moisture content level.
 8. In a dryer control according to claim 1, wherein the control includes means for limiting the voltage across the sensor to a DC voltage of relatively low magnitude so that the sensor can be connected into an integrated circuit.
 9. Dryness sensing apparatus for controlling the operation of the drying means of a laundry appliance, comprising: a dryness sensor including a pair of spaced electrodes for contacting an article of fabric undergoing drying, said electrodes connected across an electrical supply, a diode connected to one of said electrodes and a capacitor connected between said diode and the other of said electrodes which is connected to a reference potential of the electrical supply, said diode effective to block static signals of one polarity and pass via said capacitor static signals of the opposite polarity to the supply reference, means for establishing a desired moisture content level, and means connected to the junction of said diode and said capacitor for providing a control signal in response to the detection of the desired moisture content level; and means connected to said dryness sensor and operable in response to said control signal to terminate operation of the drying means.
 10. A dryness sensing apparatus according to claim 9, wherein said means for establishing a desired moisture content level includes adjustable means for changing the desired moisture content level.
 11. A dryness sensing apparatus according to claim 9, wherein said means for providing a control signal includes adjustable means for varying its sensitivity to the sensed moisture content level.
 12. A dryness sensing apparatus according to claim 9, wherein there is a series of time delay circuits connected between said dryness sensor and said means for terminating operation of said drying means to extend the drying time by selected intervals, and wherein said means for providing a control signal includes means for applying periodic reference signals to said series of time delay circuits.
 13. A dryness sensing apparatus according to claim 9, wherein said means for establishing a desired moisture content level comprises means for adjusting the duration of a time period wherein if no moisture signal is received by the dryness sensor from the fabric undergoing drying by the end of the time period, the drying cycle is terminated.
 14. A dryness sensing apparatus according to claim 9, wherein said means for terminating operation of the drying means comprises adjustable means for providing selected delay times for terminating drying beyond that drying time elapsed upon sensing of the desired moisture content level.
 15. A dryness sensing apparatus according to claim 14, wherein said adjustable means includes means for generating delayed control signals, means for selecting the delay time of said control signals, and means for interposing said adjustable means between said means for providing a control signal and the drying means. 